1. Field of the Invention
The present invention relates to an outer shell structure of a strut type shock absorber disposed between the body of a vehicle such as a four-wheeled vehicle and an axle thereof to damp vibrations from the surface of a road.
2. Description of the Prior Art
Between the body of a four-wheeled vehicle and an axle thereof is suspended a shock absorber for mitigating the transfer of vibration to the vehicle body side to ensure a stable running of the vehicle independently of running conditions, changes in the state of a road surface, etc. As shock absorbers of this type there are known, for example, those disclosed in Japanese Utility Model Publication No. 32035/1983, Japanese Utility Model Laid Open No. 16194/1980.
For example, out of the above conventional shock absorbers, the one disclosed in Japanese Utility Model Publication No. 32035/1983 has the structure shown in FIG. 3 attached hereto.
In FIG. 3, the reference numeral 1 denotes a cylinder; the numeral 2 denotes a piston provided with a damping force generating mechanism which piston partitions the interior of the cylinder 1 into a rod-side chamber and a piston-side chamber 4; numeral 5 denotes a piston rod; numeral 6 denotes an outer shell which encloses the outside of the cylinder 1 to define a reservoir chamber 7; numeral 8 denotes a base valve for imparting a damping force to a hydraulic oil flowing between the reservoir chamber 7 and the piston-side chamber 4; and numeral 9 denotes a bearing portion which closes the upper ends of the rod-side chamber 3 and the reservoir chamber 7 and holds the piston rod 5 for hermetic entrance and exit of the piston rod with respect to the interior of the cylinder 1. Further, numeral 10 denotes a lower cap provided at an end of the cylinder 1 so as to enclose the base valve 8, and numeral 11 denotes a knuckle bracket which supports the outer periphery of the lower end of the outer shell 6 and which is mounted on the axle side, the knuckle bracket 11 and the lower cap 10 being integrally connected with each other through a lower weld portion 12. Numeral 13 denotes a spring guide and numeral 14 denotes a seam weld portion. In order to obtain an optimum strength, i.e., strength against a bending moment load, of the portion of the outer shell 6 opposed to the knuckle bracket 11, despite of a light weight thereof, the outer shell 6 is smaller in its thickness on the side of the seam weld portion 14 and is sufficiently large in its thickness on the lower weld portion 12 side, according to a bending moment load distribution. As a whole, the outer shell is formed as a tapered pipe to attain the reduction in weight thereof.
In such conventional shock absorber, at the time of extension of the piston rod 5, the hydraulic oil in the rod-side chamber 3 flows to the piston-side chamber 4 through the damping force generating mechanism in the piston 2, and an extension-side damping force is generated at this time. On the other hand, during the compression stroke, the hydraulic oil in the piston-side chamber 4 flows to the rod-side chamber 3 through the above damping force generating mechanism, and at this time the hydraulic oil in the above stroke is allowed to flow between the piston-side chamber 4 and the reservoir chamber 7 through the base valve 8 to generate a compression-side damping force.
Since the conventional shock absorber is constructed as above, it is necessary to fabricate the outer shell 6 as a tapered pipe like the above or, if necessary, as a stepped pipe by drawing, thus requiring the use of special die and plug, resulting in that not only large-scaled equipment and power and plant investment are required but also the processing time and cost are increased.